基于内腔布儒斯特双轴锥棱镜的掺镱光纤激光器的径向偏振模振荡

实验采用一个内腔布儒斯特双轴锥棱镜,在掺镱多模双包层光纤激光器中实现了径向偏振光振荡,并在长2 m的增益光纤中获得了高达6.2 mW的功率输出.研究揭示了从光纤激光器振荡中获得径向偏振光的新途径.然而,该激光器输出的径向偏振光的光强分布并不很均匀,且偏振消光比较低,需要进一步改进.     

Generation of radially polarized mode in Yb fiber laser by using a dual conical prism

For the first time to our knowledge, a radially polarized beam is generated in an Yb-doped multimode double-clad fiber laser by using an intracavity dual conical prism. Up to 6.2 mW of output power is obtained from a 2 m long gain fiber with 7.4% slope efficiency. This research opens a new window to obtaining a radially polarized beam directly from an active fiber.     

Converging-axicon-based radially polarized ytterbium fiber laser and evidence on the mode profile inside the gain fiber

The radially polarized mode is achieved from an active Yb fiber by utilizing of an intracavity converging axicon, where the axicon acts as a TM(01) mode selector based on not only its Brewster convex surface but also the distance between its vertex and plane output coupler. The polarization state of the annular laser beam is checked by using a home-made eight-hole aperture. Furthermore, an uncoated plane glass plate is inserted into the cavity, and the reflected beam points to the existence of an annular lasing mode inside the gain fiber. The issues for developing high-power radially polarized fiber lasers also are considered.     

可调谐激光器腔内色散棱镜及其组合

分析了色散棱镜的特性及其顶角设计问题。讨论了色散棱镜和扩束棱镜在布鲁斯特角入射状态下，可组合使用的形式及单程角色散。提出将色散棱镜与扩束棱镜组合使用，可减少色散棱镜个数而获得更大角色散的方法。并据此设计了两个色散棱镜组，在Ｔｉ∶Ｓ激光器中得到实际使用。     

Solid-state interferometry of a pentaprism for generating cylindrical vector beam

We demonstrated the generation of a cylindrical vector laser beam using a pentaprism interferometer. The solid-state interferometer was made up of a trapezoid and right-angle prism, whose hypotenuse face was implemented with a polarization beam splitter coating that split a rotated TEM₀₁ mode beam into two orthogonal polarizations. The Ppolarized beam was reflected inside the prism twice, allowing a mode pattern without inversion; however, the Spolarized beam was reflected once resulting in mode patterns that form P-polarized beams rotated by 90°. We also held the phase shift of the two beams to zero by use of a phase shifter, thus the output of the superimposed beam was a radially polarized beam. We demonstrated the mode pattern and polarization purity of the output beam through the use of this configuration.     

Description of a radially polarized Laguerre-Gauss beam beyond the paraxial approximation

Fifth-order corrected expressions for the fields of a radially polarized Laguerre-Gauss (R-TEM(n1)) laser beams are derived based on perturbative Lax series expansion. When the order of Laguerre polynomial is equal to zero, the corresponding beam reduces to the lowest-order radially polarized beam (R-TEM(01)). Simulation results show that the accuracy of the fifth-order correction for R-TEM(n1) depends not only on the diffraction angle of the beam as R-TEM(01) does, but also on the order of the beam.     

Production of radially or azimuthally polarized beams in solid-state lasers and the elimination of thermally induced birefringence effects

Production and amplification of radially and azimuthally (tangentially) polarized laser beams are demonstrated. Based on the different focusing between radially and tangentially polarized light in thermally stressed isotropic laser rods, Nd:YAG laser oscillators were developed to produce low-loss stable oscillation in a single polarization. Pure radially polarized light at 70 W with M2 = 2 and on-axis impure radially polarized light at 150 W with M2 = 2.5 were achieved. The radially polarized beams were then amplified while good beam quality and polarization purity were retained. Complete elimination of thermal-birefringence-induced aberrations was demonstrated. This should allow much better beam quality from rod-based high-power lasers.     

Generation of a radially polarized laser beam by use of the birefringence of a c-cut Nd:YVO4 crystal

We demonstrated the generation of a radially polarized laser beam from an extremely simple laser resonator including a c-cut Nd:YVO4 crystal as a laser medium. The oscillation in the radial polarization was based on the optical path difference between an extraordinary ray and an ordinary ray induced by the birefringence of the crystal. By simply adjusting the distance between two cavity mirrors, only the extraordinary ray became stable for the oscillation, resulting in the generation of a radially polarized beam. The beam was very stable even at low power output and is expected to be a promising radially polarized laser source because of its excellent simplicity.     

Radially polarized 3 kW beam from a CO2 laser with an intracavity resonant grating mirror

A 3 kW radially polarized beam is generated from a CO(2) laser by means of a resonant grating mirror. The design results and spectral characterization of a broadband polarizing mirror are presented as well as the mirror's operation in a CO(2) laser resonator. In a long-term experiment a radially polarized beam with a power of 2.7 kW was observed for several hours, proving the high stability of this polarizing scheme.     

Simple Nd:YAG laser generates vector and vortex beam

We report a simple Nd:YAG laser that emits radially polarized beam with helical wavefront. The laser cavity consists of a piece of laser crystal and a plane output coupler, and there is no additional polarization component inside it. The pump light is converted into annular profile through de-focal coupling into a multi-mode fiber. For the continuous-wave(CW) operation, the laser emits radially polarized vortex beam, and it is observed that the helical wavefront of the laser beam is switched from right handedness to left handedness when the output coupler is tilted slightly. For the Q-switched operation under the insertion of a Cr4t:YAG saturable absorber inside the cavity, we obtain radially polarized outputs with left-handedness helical wavefront. By tilting the laser crystal slightly, the laser output switches to azimuthal polarization at pump power larger than 4.5 W and left-handedness helical wavefront of laser beam is preserved.     

A mirror-free cavity configuration for a CW ring dye laser

A new cavity configuration without mirrors is described for a CW ring dye laser. The cavity design is based on a new type of focusing prism which uses the Brewster angle of incidence and total internal reflection. Special roof prisms allow wavelength tuning. All of these elements are made from uncoated quartz thus allowing dye laser operation over a large range of wavelengths. CW operation as well as synchronously pumped mode locked operation with intracavity doubling is reported using the Rhodamine 6G dye.     

Single higher-order transverse mode operation of a radially polarized Nd:YAG laser using an annularly reflectivity-modulated photonic crystal coupler

We demonstrate single higher-order transverse mode operation of a radially polarized Nd:YAG laser by using a polarization-selective and reflectivity-modulated output coupler. A narrow annular region with low reflectivity fabricated in a photonic crystal mirror behaves so as to select a higher-order transverse mode of a cylindrically symmetric laser beam. A double-ring-shaped radially polarized TM(02) mode beam is stably generated.     

Polarization properties in a prism laser gyro with mechanical dither bias

<正>Theoretical analysis and experimental research on the polarization properties of output light in gyro are carried out to investigate the phenomenon that the amplitude of an output voltage signal is modulated by dither bias in laser gyros consisting of totally reflecting prisms.Taking the effect of prism stress birefringence into account,an analytical formula of the output light intensity in the gyro and the relationship between the polarization parameter and the amplitude modulation of the output signal are obtained and discussed.For the first time,the polarized power value of the output light is adopted as a basis to estimate the output signal amplitude fading extent of laser gyros.Experimental results demonstrate that when the value of polarized power of output light is below 25.5%of that in ideal static case,the standard error is over 0.0337 dBm,and the displacement extent of the prism is higher than 53%of the radius of the beam waist in the gyro cavity,the amplitude modulation extent of gyro output signal can reach up to 16%,which badly influences the measurement accuracy of the laser gyro.Using this polarized power detecting measurement method can repair the gyro immediately during its fabrication process,improve the testing and production efficiency and shorten the product development cycle.     

星间激光通信光束微弧度跟瞄性能检测装置的设计原理

基于矢量折射定理,研究了透射光束通过双棱镜实现微弧度量级偏转的设计原理,解决了星间激光通信精跟瞄检测的难题。推导了正交双棱镜实现光束偏转的精确公式,提出以水平张角和垂直张角表达光束视场,并说明了单棱镜实现光束偏转的一般情况。根据设计指标和计算结果确定了棱镜的主要参量,进而对光束的偏转结果进行了数值模拟。最后的实验结果与模拟结果基本一致。结果表明:取棱镜棱角α为4°时,棱镜每旋转1′,透射光束变化约1μrad;分别控制双棱镜在其最小偏向角一侧小角度偏转,可以实现光束在水平方向和垂直方向500μrad范围内的精确扫描,装置的扫描精度可以达到0.2μrad。     

Effect of polarization on femtosecond laser pulses structuring silicon surface

Arrays of conical-like spikes can be formed on silicon surface after irradiated with femtosecond laser pulses in ambient of SF₆ or N₂. In this article, we report our observations on how the shape of the spikes formed on silicon surface varies with the polarization of laser beam. The experimental results show that, with circular polarized laser irradiation, the shape of the spikes is conical; however, with linearly polarized laser irradiation, the spikes show elliptic conical shape, and the long-axes are perpendicular to the direction of the polarization of laser beam. The asymmetric shape of spikes produced by linearly polarized laser beam can be explained by considering the polarization dependence of Fresnel-refraction.     

Electron acceleration to GeV energy by a radially polarized laser

We present a relativistic single particle simulation of vacuum acceleration of an electron by a high-intensity radially polarized laser beam. The inherent complete symmetry of radially polarized laser beam leads to improvement in the trapping and acceleration of an electron so that an electron can be accelerated to the level of GeV. In addition, the external magnetic field further enhances the electron acceleration. Hence, an electron of ultrahigh energy was observed. The strong correlation between final electron energy and scattering angle is discussed.     

非均匀关联径向偏振部分相干光的产生

从理论和实验两方面对非均匀关联径向偏振部分相干光的产生进行了研究.理论上,基于相位关联与相干度的联系,推导出了非均匀关联径向偏振部分相干光的2×2阶交叉谱密度矩阵及相干度分布.实验上,利用一个相位型液晶空间光调制器的不同区域,对入射的完全相干的径向偏振光的两个正交偏振分量分别加载随机相位调制,并实验测量了这种光束的相干度分布及其对光强分布的影响.实验结果验证了光束相干度的非均匀关联结构,并且通过改变随机相位的高斯调制半宽可以改变光束的相干性分布.研究表明,随着随机相位的高斯调制半宽的增加,光束中两点间的相干度逐渐减小,其光强分布由圆环状逐渐变化为类平顶的光强分布.这种非均匀关联的径向偏振部分相干光在激光微操纵和材料加工等领域具有一定的潜在应用价值.     

折叠式角锥棱镜谐振腔的偏振特性理论与实验研究

建立了角锥棱镜的偏振模型,分析了角锥棱镜对入射线偏振光的偏振态的影响,分析表明角锥棱镜的单个入射区域存在特殊的偏振方向,该方向的线偏振光被角锥棱镜反射后仍然是线偏振光。利用角锥棱镜的该特性设计了腔内存在线偏振光振荡的角锥棱镜激光谐振腔,能够使用电光开关调Q,在振动环境中具有较好的抗失调稳定性。研制了激光器样机并进行了实验,在重复频率为10 Hz时,输出激光单脉冲能量大于300 mJ,光束质量因子β值在2左右,实验结果也表明角锥棱镜的棱和顶点并不影响输出激光的光束质量。     

Efficient conversion of a radially polarized beam to a nearly Gaussian beam

We demonstrate an efficient method for transformation of a radially polarized Laguerre-Gaussian beam to a nearly Gaussian beam with much higher beam quality. The method is based on separation of the radially polarized mode into two degenerate modes and coherent addition of the modes after phase flattening. We transformed a high-power Nd:YAG radially polarized (0,1)(*) Laguerre-Gaussian beam with M(2)=2.52 and power of 30 W into a nearly Gaussian beam with M(2)=1.3. As a result, the brightness increased by a factor of approximately 2.5.     

Generation of radially polarized Ti:sapphire laser beam using a c-cut crystal

First, it is demonstrated that with a c-cut Ti:sapphire crystal the generation of a nonpolarized laser beam is possible, in contrast to the conventional a-cut Ti:sapphire crystal, which produces a linearly polarized beam. Second, the generation of a radially polarized Ti:sapphire laser beam is demonstrated in combination with a c-cut YVO(4) crystal used as a selector of radial polarization.